1. Field of the Invention
The present invention relates to a vehicular navigation display system.
2. Related Art
In prior art vehicular navigation systems using a display with 320 pixels per horizontal line, the pixels are read out and displayed by timing in accordance with a clock suitable for producing the 320 pixels.
As shown in FIG. 7, an electronic control unit (ECU) for a prior art vehicular navigation system includes a central processing unit (CPU) 1, various input/output (I/O) units 2, a program memory 3, a work memory 4, an external memory unit 5, an application-specified IC (ASIC) 6, an image data memory 7, a video signal interface 8 and a display 9 with a horizontal width of 320 dots or pixels. Numeral 11 designates a system bus.
From data read out of the external memory unit 5, the CPU 1 produces suitable image data for the display screen 9 and writes the image data in the image data memory 7 through the ASIC 6. The ASIC reads out horizontal lines of the image data in the memory 7 and converts the data to RGB video signals. These RGB video signals along with horizontal and vertical sync signals generated by the ASIC are applied to the display 9 to display a plurality of 320 pixel (dot) horizontal lines. This prior art display 9 has an aspect ratio of 4:3 (horizontal:vertical).
The clock driving the ASIC is suitable for the 320 horizontal dot display. As illustrated in FIG. 8, the period between horizontal synchronizing signals is 63.5 .mu.s and the RGB video data portion (320 dots) of this period is 50 .mu.s in duration. In this example, each dot interval is 156 ns (1/320 of 50 .mu.s) requiring a display rate of 6.4 MHz. The clock driving the ASIC has a frequency four times higher than the display rate or 25.6 MHz.
Recently, some navigation systems have been designed to utilize a display with a wider aspect ratio of 16:9 (horizontal:vertical). This wider aspect display screen has 400 dots or pixels per horizontal line. Although the period between horizontal synchronizing signals and the period in each horizontal line for RGB data remain the same, the clock frequency is increased to read and display 400 dots per horizontal line.
In the prior art, different electronic control units (ECUs) are required for the 320 horizontal dot and 400 horizontal dot displays. This results in higher costs since manufacturing separate ECUs for the corresponding 320 horizontal dot and 400 horizontal dot displays costs more than manufacturing a single ECU.